1. Field of the Invention
The present invention relates to tape readers generally and, more particularly, to a bias current change for a MR reader during a read only operation.
2. Background Art
In a tape environment, a tape reader is required to have sufficient amplitude to overcome the inherent noise present in the tape drive. Write-to-read signal feedthrough is one of the largest noise sources in the system. The write-to-read signal feedthrough noise is present during a write operation when a read verify operation is occurring simultaneously with the write operation. The write-to-read signal feedthrough noise is not present during a read only operation.
The ongoing push to implement larger tape cartridge capacities has resulted in higher recording densities and decreased read track widths. The combination of higher recording densities and decreased read track widths causes a decrease in reader signal amplitude. Implementation of more sensitive magnetoresistive (MR) readers can partially improve the reader signal amplitude. However, a negative result of the more sensitive MR readers is that the higher sensitivity MR readers tend to operate at higher read head element temperatures since the higher sensitivity is typically implemented in connection with an increased read head bias current density.
In soft adjacent layer (SAL) biased MR read heads, the readback (or read) signal amplitude increases with increased bias current. However, Joule heating of the MR read head element causes the MR read head temperature to increase with the increased bias current. Other performance parameters such as amplitude symmetry tend to be insensitive to the bias current when the SAL film is saturated.
MR disk heads are known to exhibit a read signal fluctuation due to cooling of the MR reader when the MR head comes in close proximity to the disk (see, for example, H. Tiam, C-Y. Cheung and P-K. Wang, xe2x80x9cNon-Contact Induced Thermal Disturbance of MR Head Signalsxe2x80x9d, IEEE Trans. Magn., Vol. 33, No. 5, pp. 3130-3132, 1997 and S. Zhang and D. Bogy, xe2x80x9cVariations of the Heat Flux Between a Slider and Air Bearing when the Slider Flies Over an Asperityxe2x80x9d, IEEE Trans. Magn., Vol. 34, No. 4, pp. 1705-1707, 1998, which are hereby incorporated by reference in their entirety). MR tape read heads exhibit a similar read signal fluctuation phenomenon when the tape comes in closer contact with the MR read head (see, for example, R. H. Dee and R. F. M. Thornley, xe2x80x9cThermal Effects in MR Heads for Tape Applicationsxe2x80x9d, IEEE Trans. Magn., Vol. 27, No. 6, pp. 4704-4707, 1991, which is hereby incorporated by reference in its entirety). The read signal fluctuation often causes errors in the read channel signal. The read signal fluctuation is made worse when the MR read head element temperature is higher. In addition, elevated temperatures can reduce MR read head element lifespan.
A conventional tape drive can experience reading blocks in error due to the cooling effect. MR heads that operate at higher temperatures due to process variation during head manufacturing are more prone to reading blocks in error due to the cooling effect. In some conventional tape drives, the read signal fluctuations increase the block error rate and lead to reduced system margins. The read signal fluctuation due to elevated temperatures can be particularly problematic when reading legacy tapes where the system margin has been reduced due to system constraints.
Thus, there exists a need for an apparatus and/or a method for reducing the temperature of the read head element. The reduced temperature read head may be advantageously implemented in MR head applications. The reduced temperature read head may reduce block error rates. The reduced temperature read head may improve system margins. The reduced temperature read head may provide improved MR read head lifespan. The reduced temperature read head may be advantageously implemented during read only operations. The read only operations where the reduced temperature read head may be implemented may include legacy read operations, normal (i.e., standard, non-legacy) read operations, and/or error recovery procedures or operations.
Accordingly, the present invention provides an improved apparatus and/or method for reducing tape read head temperature where the bias current that is presented to the read head is at a lower amplitude during at least one mode of operation (e.g., at least one read only mode) than during at least one other mode of operation (e.g., a write/read mode), thereby reducing block error rates.
According to the present invention, an apparatus is provided comprising a tape read head bias signal control circuit configured to present to a tape read head a first amplitude bias signal in response to at least a first control signal and a second amplitude bias signal in response to at least a second control signal. The second amplitude is lower than the first amplitude.
Also according to the present invention, a method for reducing a tape read head temperature is provided comprising presenting a first amplitude bias signal to a tape read head during at least a first mode of operation and presenting a second amplitude bias signal to the read head during at least a second mode of operation. The second amplitude is lower than the first amplitude.
Further, according to the present invention, an apparatus is provided comprising a tape read head and a tape read head bias signal control circuit. The tape read head bias signal control circuit may be configured to present a first amplitude bias signal in response to at least a first control signal and a second amplitude bias signal in response to at least a second control signal to the tape read head. The second amplitude is lower than the first amplitude.
Also according to the present invention, a method for reducing a tape read head temperature is provided comprising providing a tape read head bias signal control circuit configured to present to a tape read head a first amplitude bias signal in response to at least a first control signal and a second amplitude bias signal in response to at least a second control signal. The second amplitude is lower than the first amplitude.
Still further according to the present invention, an apparatus is provided having a reduced tape read head temperature. The apparatus includes means for presenting a first amplitude bias signal to a tape read head during at least a first mode of operation and means for presenting a second amplitude bias signal to the read head during at least a second mode of operation. The second amplitude is lower than the first amplitude.
The above features, and other features and advantages of the present invention are readily apparent from the following detailed descriptions thereof when taken in connection with the accompanying drawings.